The present invention relates generally to the field of moving picture compression technique. More specifically, the invention relates to a motion vector estimating system, which carries out, at low costs, the operation for a motion vector estimation used for a moving picture compression.
In general, moving picture estimation is essential to moving picture compression technique used for video telephones and so forth. In this process, the costs in operation and electric power consumption are greatly increased as the search range is increased so as to correspond to generalized patterns. In the uses for mobile video telephones and so forth, there has been provided technique for cutting an image information on a particular object such as a face of a person, out of the whole picture to transmit the cut image information in order to reduce the amount of information. However, in the present circumstances, it is technically difficult to cut a specific object out of a picture with a natural picture for a background, unlike a picture taken in a studio.
In the moving picture compression or the like, motion vectors are extracted by a process, which comprises the steps of: dividing the screen of an inputted current image into partial regions (each of which will be hereinafter referred to as a "macro block"); shifting the coordinates of the macro blocks by (+x, +y); accumulating the luminance signal differences (which will be hereinafter referred to as "SAD") from the screen of a reference image at that time for each of the picture elements (pixels) in the macro block; and adopting, as a motion vector, (x, y) when the accumulated value is minimum. In this operation, the load increases in proportion to the square of the region of search for the motion vectors. Therefore, when motion vectors are extracted for each of the macro blocks which are presented in the whole screen, it is difficult to increase the region of search for motion vectors.
On the other hand, unlike general motion vector estimations, in the case of a specific image pattern represented by a simple picture feature, for example, in the case of double circles of violet and yellow, it is easy to search the whole screen to determine the presence of the feature on the screen or to identify the global coordinates of the feature. The vector prepared by tracing the global positions of the characteristic pictures in sequential pictures will be hereinafter referred to as a "global motion vector" for convenience.